1. Field of the Invention
This invention relates to an optical head for coping with plural optical recording mediums of different kinds and to an optical disc device for recording and/or reproducing signals for plural optical recording mediums of different kinds using this optical head.
2. Description of Related Art
Up to now, a replay-only optical disc, termed a compact disc (CD), or a write-once optical, disc termed a CD-R (Compact Disc Recordable), has been put to practical utilization. These optical discs have been in widespread use because the discs are superior in mass-producibility and can be manufactured at low cost, while being usable for recording or reproducing the information in high stability.
Meanwhile, in these optical discs, the recent tendency is towards higher recording capacity. Amidst this tendency, the DVD (Digital Versatile Disc/Digital Video Disc) which, despite the fact that its outer diameter is equal to that of the CD, has a drastically improved recording capacity, such that data corresponding to an entire motion picture can be stored therein with a picture quality comparable to a current television broadcast, has been developed and put to practical utilization. In this DVD, a laser light shorter in wavelength than the laser used for a CD is used for recording and/or reproducing the information in order to elevate the recording density to increase the recording capacity.
As to an optical disc device employing a so-called compatible optical disc as a recording medium, such an optical disc device has been developed in which there is provided an optical head capable of recording and/or reproducing not only the information for the DVD but also that for the CD or CD-R.
Meanwhile, in the optical head capable of accommodating both the CD or the CD-R and the DVD, the optical system for the CD or the CD-R desirably has as many portions in common with the optical system for the DVD as possible, in order to reduce the overall size of the head or to lower the production cost.
In order to meet this demand, development of an optical head having a so-called double-wavelength semiconductor laser for selectively radiating the laser light for coping with the CD or the CD-R and the laser light for coping with the DVD is underway. In the double-wavelength semiconductor laser, a light source for radiating the laser light designed for coping with the CD or the CD-R and a light source for radiating the laser light designed for coping with the DVD are arranged in proximity to each other and are housed in the same package.
In such optical head, it also is proposed to arrange an optical component in the form of a flat parallel plate in an optical path obliquely and to impart the function of a beam splitter to this optical component. If the optical component in the form of a flat parallel plate is used as a beam splitter, the return light beam of respective laser light beams transmitted through this optical component and subsequently reflected back from the optical disc is subjected to astigmatic aberration. If this astigmatic aberration is utilized to detect focussing error signals, there is no necessity for providing dedicated optical components, thus simplifying the structure.
However, in this double-wavelength seimconductor laser, there are imposed limitations on the mounting position of a photodetector adapted for receiving the return beams of the respective light beams reflected back from the optical disc, such that, if the respective light sources and the light receiving portions are not arranged at proper positions, focussing error signals cannot be detected properly with the aid of astigmatic aberration.
It is, therefore, an object of the present invention to provide an optical head adapted for coping with plural optical recording mediums of different kinds and which enables focussing error signals to be detected properly by the astigmatic method while enabling the overall size of the optical head to be reduced. It is another object of the present invention to provide an optical disc device which enables signals to be recorded and/or reproduced properly to or from the plural optical recording mediums of different kinds using the optical head.
In one aspect, the present invention provides an optical head for coping with a plurality of optical recording mediums of different types, including light radiating means including a first light source for radiating the first laser light and a second light source for radiating the second laser light having a wavelength different from that of the first laser light, the first and second light sources being housed in the same package, light converging means for converging the laser light from the light radiating means towards the optical recording medium, a beam splitter substantially in the form of a flat plate for separating the optical path of the laser light proceeding towards the optical recording medium from that of the laser light reflected from the optical recording medium and for producing astigmatic aberration in the return laser light and light receiving means for receiving the return laser light reflected back from the optical recording medium. The relative positions of the first and second light sources of the light radiating means are set so that a straight line interconnecting a spot position of the first laser light illuminated on the optical recording medium and a spot position of the second laser light illuminated on the optical recording medium will be in a range of 45xc2x115xc2x0 with respect to a recording track of the optical recording medium. The light receiving means includes a pair of light receiving sections arranged substantially parallel to a straight line projected on the optical recording medium, the straight line being a straight line interconnecting a spot position of the first laser light illuminated on the optical recording medium and a spot position of the second laser light illuminated on the optical recording medium. Each of the light receiving sections is split into four portions by a splitting line substantially parallel to the recording track on a signal recording surface of the optical recording medium and a splitting line substantially perpendicular thereto.
In another aspect, the present invention provides an optical head for coping with a plurality of optical discs of different types, including a semiconductor laser including a first light source for radiating the first laser light and a second light source for radiating the second laser light having a wavelength different from that of the first laser light, the first and second light sources being housed in the same package in proximity to each other, with the semiconductor laser selectively emitting the first laser light or the second laser light depending on the disc type, an objective lens for converging the laser light from the semiconductor laser on the optical disc, a beam splitter for separating the optical path of the laser light proceeding towards the optical disc and that of the laser light reflected from the optical disc from each other, and a light receiving element for receiving the return laser light reflected back from the optical disc. The beam splitter generates astigmatic aberration in the return light beam. The relative positions of the first and second light sources of the light radiating means are set so that a straight line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light illuminated on the optical disc will be in a range of 45xc2x115xc2x0 with respect to a recording track of the optical disc. The light receiving element includes a plurality of light receiving sections obtained on splitting by a splitting line substantially parallel to the straight line projected on the light receiving unit, the straight line being such a line interconnecting the spot position of the first laser light illuminated on the optical disc and the spot position of the second laser light similarly illuminated on the optical disc. Each of the light receiving sections is split into four portions by a splitting line substantially parallel to the recording track on a signal recording surface of the optical recording medium and a splitting line substantially perpendicular thereto, to generate focussing error signals by an astigmatic method based on respective light receiving signals of the paired light receiving portions.
In a further aspect, the present invention provides an optical disc device for recording and/or reproducing signals in association with a plurality of optical discs of different types, in which the device includes a spindle motor for rotationally driving the optical disc, an optical head adapted for coping with the plural optical discs of different types and a signal processing circuit for generating playback signals and control signals based on signals detected by the optical head. The optical head includes light radiating means having a first light source for radiating the first laser light and a second light source for radiating the second laser light having a wavelength different from that of the first laser light, the first and second light sources being housed in the same package, the light radiating means selectively radiating the first laser light or the second laser light responsive to the type of the optical disc, an objective lens for converging the laser light from the light radiating means towards an optical disc, a beam splitter for separating the optical path of the laser light radiated from the light radiating means into the optical path of the laser light proceeding towards the optical disc and the optical path of the laser light reflected from the optical disc and a light receiving element for receiving the return laser light reflected back from the optical disc.
The relative positions of the first and second light sources of the light radiating means are so set that a straight line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light illuminated on the optical disc will be in a range of 45xc2x115xc2x0 with respect to a recording track of the optical disc. The light receiving element includes a plurality of light receiving portions obtained on splitting by a splitting line substantially parallel to a straight line projected on the light receiving means, the straight line being a line interconnecting a spot position of the first laser light illuminated on the optical disc and a spot position of the second laser light similarly illuminated on the optical disc. Each of the light receiving portions is split into four portions by a splitting line substantially parallel to the recording track on a signal recording surface of the optical recording medium and a splitting line substantially perpendicular thereto.
In the optical head according to the present invention, focussing error signals can be detected properly by the astigmatic aberration method, even with the use of a light radiating element selectively radiating laser light beams designed for coping with plural optical recording mediums, such as CD-R and DVD, thus enabling the overall size of the optical head to be reduced.
With the optical disc apparatus, according to the present invention, by employing this optical head, focussing control can be achieved properly to provide for proper focussing control and proper recording and/or reproduction of signals on or from the optical disc. On the other hand, the overall size of the apparatus can be reduced by reducing the optical head size.